Audiological screening method and apparatus

ABSTRACT

An audiological screening and testing method for newborns and infants employing audiological screening via statistical phase analysis of otoacoustic emissions in response to acoustic stimili.

BACKGROUND OF THE INVENTION

1. Field

This invention relates to audiological screening and testing methods.More particularly, it relates to a phase analysis system method andapparatus employing audiological screening via statistical phaseanalysis of otoacoustic emissions (OAE's), which are signals that aregenerated by the hair cells of a functioning inner ear in response toacoustic stimuli as a result of the non-linear properties of thecochlear amplifier.

2. State of the Art

Various audiological screening and testing methods are known. For thehearing testing of infants and small children, measurement systems basedon the principle of evoked potentials or otoacoustic emissions viasignal averaging and individual evaluation by a tester reviewing variouswave pattern hearing responses on a display screen are often employed.Because these types of examinations are expensive, and require skilledevaluators, the results often are dependent upon the subjective skillsof the evaluator. To overcome these subjective testing limitations,various signal display and evaluation apparatus, such as Kemp,PCT/GB/00030, published Aug. 7, 1981, entitled "Hearing Faculty TestingApparatus, were developed. These conventional display methods employmethods of frequency and amplitude analysis of otoacoustic emissions(OAE's) signals generated by the inner ear in response to various tones.The frequency and amplitude of the OAE signals are picked up by amicrophone and fed into a wave pattern display for measurement andmanual or statistical analysis by an operator, see Zoth, DE 4441127A1published May 23, 1996. These methods and devices may also employaveraging, where a number of signal intervals following the stimulation("sweeps") are added synchronously with the stimulus, thus improving thesignal-to-noise ratio until the emissions are detectable. These othermachines thus require an experienced examiner to make a decision basedon a number of objectives and subjective criteria such as the frequencyspectrum, typical curve morphology and time distributions of themeasured signals. The danger in using a normal averaging procedure isthat any waveform can be produced by chance. To guard against this,other commercial systems have added additional features such ascorrelation of two quasi-simultaneous measurements. While this hasproven valuable, the amount of correlation depends on the frequencyspectrum of noise and signal, which differs from one measurement toanother. As a consequence, a given correlation cannot be usedexclusively as the criterion for the presence of emissions.

The invention described below provides an improved otoacoustic emissionstesting and screening apparatus and method based on a phase analysissystem of an analogue signal to provide a "pass"/"fail" or"pass"/"refer" type of response, which is more suitable for automatedevaluation without the need for highly trained evaluators.

SUMMARY OF THE INVENTION

The impact of undetected hearing loss in a child is life long in that itinterferes with the normal development of communication skills. Earlydetection of hearing loss allows early intervention, which can reducethe adverse effects of hearing impairment on speech and languagedevelopment. Sensitivity and specificity for conventional screeningprocedures carried out in early childhood have been shown to be low.They do not identify all children with significant hearing loss andresult in high referral rates. Conversely, diagnostic procedures such asevoked response audiometry are expensive, time-consuming, and requireprofessional expertise to administer the test and interpret the results.

The present invention employs screening based on otoacoustic emissionsand fills the gap between conventional screening procedures and evokedresponse audiometry. It is the only emission-based screening device,which can reliably be used by testers without professional training.This makes it ideally suited for use by physicians and nurses in apediatric or general practice setting, by personnel in well-babynurseries, and even by health visitors in home settings.

The method of the invention for audiological screening of infants andnewborns comprises first generating a stimulus with acoustictransmitters in both ear canals of the infant or newborn, and thencollecting any transient evoked and distortion product otoacousticemissions generated by the cochlea in each ear canal in response to thestimulus with microphone means to generate a frequency mixed productelectronic signal. The frequency mixed product electronic signal fromthe microphone means and the stimulus frequencies are then inputted intoa computer processor. This mixed product electronic signal is amplifiedwith an input amplifier and computer analyzed with the aid of afrequency analyzer and phase analyzer to separate the frequenciescomprising the mixed product electronic signal into separate backgroundnoise signal components and otoacoustic emissions signal components. Acomputer calculated statistical evaluation of the otoacoustic emissionssignal components with binomial statistics is then run to determine ifthe otoacoustic emissions signal responses to each stimulus are or arenot statistically significant. These statistical conclusions are thendisplayed on a computer display.

The apparatus of the invention is a miniaturized hearing screeningsystem based upon the measurement of transiently evoked otoacousticemissions. It consists of a power source operably associated with twostimulus generators with the appropriate acoustic transmitters. Thefrequency product generated by the cochlea in response to the generatedstimulus is measured with the aid of a microphone. The microphonegenerates an analogue electronic signal fed to an input amplifier. Thefrequencies of the mixed products of the electronic signal are analyzedwith the aid of a frequency analyzer before employing a phase analyzer.The phase analyzer is generally employed to evaluate the 3^(rd) orderintermodulation product like (2f1-f2), where f2 is approximately equalto 1.2 times f1. This provides the greatest signal amplitude forstatistical evaluation as described more fully below. The statisticalresult is then shown on a "Pass"/"Fail" or "Pass"/"Refer" display,and/or outputted to a printer or PC.

No expertise is required to use the device properly. It is completelymicroprocessor controlled, and evaluation is done automatically by meansof a strict signal statistical criterion. This criterion reduces theprobability for a false negative result to less than 1%. The deviceworks as well in analyzing transiently evoked otoacoustic emissions(TEOAE's) and by analyzing distortion product otoacoustic emissions(DEOAE's) described below.

It is based on the measurement and analysis of otoacoustic emissions(OAE's), which are signals generated by the hair cells of a functioninginner ear in response to acoustic stimuli as a result of the non-linearproperties of the cochlear amplifier. These OAE signals are measured andassessed in two essential steps:

Step 1. Separation of the Stimulus from the Signals to be Measured

Various routes are followed for this:

Separation in the time range:

If the stimulus is very short (transient stimulus), the measurementwindow can be selected such that the passive echo from the auditorycanal has already decayed again when tie response is recorded. Thisguarantees that the acoustic signals measured consist only ofstimulus-independent sounds and, where appropriate, the OAE's evoked bythe stimulus and not of any portion of the stimulus itself or its echo.The responses picked up by the microphone and measured in this way aredesignated transient evoked otoacoustic emissions (TEOAE's).

Separation in the frequency range:

If continuous sinusoidal sounds are applied as the stimulus, the soundresponse generated by the inner ear can be separated from the stimulusby analyzing the outside the sound frequencies of the stimuli. Sinceintermodulation products of the primary frequencies are generated as aresult of the non-linearity of the functioning inner ear, the presenceof signals whose frequencies do not match ("clash") with the stimulussignals is a deciding factor in proving the integrity of the inner ear.These signals are termed distortion product otoacoustic emissions(DPOAE's). DPOAE's are generated by stimulation with two tones ofdifferent frequency. The intermodulation products generated at thecochlea are measured with a microphone, amplified and analyzed withreference to specific mixed frequencies by means of Fouriertransformation. This technique which is already known in the art coversa broad frequency range in conventional devices, but no automatedevaluation of the results is known.

Step 2. Proof of the Response

An essential feature in interpreting the acoustic signals measured isthe proof that the signal actually originates from the inner ear and isnot ambient noise. All systems currently used for such measurementsexploit the fact that the responses generated by the stimulus, bycontrast with noise, are phase-synchronous with the stimulus.Conventionally, an average technique (stimulus-synchronous averaging) isused to repeatedly amplify the signal to be measured in comparison withthe noise until it can be identified by an experienced tester as anemission. A frequently used aid is to define a measurement for the"residual noise" and to compare the averaged signal with the residualnoise. If the difference between both signals is large, a stimulussynchronous activity may be assumed.

The present invention is based on a phase analysis system describedbelow which, by contrast with the conventional methods of frequency andamplitude analysis, is suitable for automated evaluation.

Objectives of the Invention

There are two essential objectives behind the present method andapparatus for measurement and assessment of otoacoustic emissions:

Screening

For screening, it ought to be possible to discover the inner earactivity in an automated system without the judgement of an expert.Non-parametric signal statistics are necessary for this which, inaddition to the result "Emission present" also determines an exactfigure for the significance level. This enables the quality of themeasurement to be defined exactly in relation to the error rate.

Phase Analysis

Every time period evaluated contains a mixture of various signals ofdiffering frequency, amplitude and phase. These signals can be separatedfrom each other by means of a transformation in the frequency spectrum(Fourier transformation).

A properly functioning cochlea responds to sound by active movements ofthe outer hair cells. This mechanism serves two purposes: it increasessensitivity for low-level sounds, and it increases the frequencyresolution of the ear. While the inner hair cells convert the mechanicalelongation of the cochlear membrane into the action potentials in about30,000 nerve fibers, the outer hair cells amplify and tune the incomingsound. The active movement of the outer hair cells produces and resultsin mechanical energy being transmitted from the inner ear to the outerear canal via the ossicle chain and the tympanic membrane. The movementof the tympanic membrane creates sound waves in the ear canal. Thusotoacoustic emissions are a byproduct of the active function of theouter hair cells. While otoacoustic emissions often occur spontaneously,they can also be evoked by a transient acoustic stimulus and measured bymeans of a miniature microphone, which is placed in the ear canal. Theamplitude of evoked emissions is quite large in neonates (sometimescorresponding to a sound pressure level of 30 dB) and decreasescontinuously during the first years of life.

If the stimulus is very short (transient stimulus), the measurementwindow can be selected such that the passive echo from the auditorycanal has already decayed again when the response is recorded. Thisguarantees that the acoustic signals measured consist only ofstimulus-independent sounds and, where appropriate, the OAE's evoked bythe stimulus and not of any portion of the stimulus itself or its echo.The responses measured in this way are designated transient evokedotoacoustic emissions (TEOAE's).

The present device is particularly good in dealing with the followingdisorders and their transient evoked otoacoustic emissions. Transientevoked otoacoustic emissions are highly sensitive to different types ofhearing loss. The presence of TEOAE is associated with healthy,well-functioning cochleae and middle ears, while a hearing loss of 30 dBor more which is cochlear or conductive in nature will result in theabsence of TEOAE.

Conductive hearing loss is commonly caused by low eardrum motilitysubsequent to Eustachian tube dysfunction, middle ear effusion, ormalformation of outer and middle ear structures. It results in anattenuation of the transmitted acoustic signals in both directions:stimulus as well as emission conduction. Though emissions may bepresent, their amplitude is decreased to a degree that they are notdetectable. Even a mild conductive loss of 10 to 20 dB (corresponding toa signal attenuation factor 3 to 10) can make emission signalsundetectable.

Cochlear dysfunction (Cochlear hearing loss) is highly correlated withan absence of transient evoked otoacoustic emissions. No emissions areproduced in an inner ear with a broadband threshold elevation of morethan 30 dB. The outer hair cells are affected first in nearly allcochlear hearing losses. Frequency specific losses (i.e. notchaudiograms) and mild threshold elevations between 5 and 30 dB correlatewith missing emissions in a statistical but not unique way. Presence oftransiently evoked emissions indicates that peripheral hearing issufficient for speech acquisition without intervention. Some rare casesof steep audiograms have been described where emissions could be evokedby a transient stimulus in spite of cochlear dysfunction. However, sincethis type of hearing loss configuration is difficult to verify exactlywithin the first year of life, providing amplification is too difficultin most of these cases.

Retrocochlear hearing is due to the mechanism of emission production,and cannot be detected by emission measurements. Fortunately,Retrocochlear impairment is extremely rare in infants. The incidence ofRetrocochlear pathology is less than 1% of all non-central hearingdisorders.

Screening with Emissions

The method and device acts as a screening tool to prove the presence ofemissions on a well-defined level of confidence in order to make themuseful as a screening tool. Screening should only result in a "pass" or"refer". "Refer" is not necessarily equivalent to pathology--in fact itseldom is--but should serve as a criterion to undergo an audiologicfollow-up procedure. A typical testing and evaluation sequence is totest the newborns on the second or third day for transient evokedotoacoustic emissions (TEOAE). If they pass, the newborns aredischarged. If they fail, they are re-tested within 15 days. Again, ifthey pass, they are discharged, but if they fail, they are retestedagain within the third month. If the fail again, they are then referredto habilitation therapy.

Signal Processing for TEOAE

The method and apparatus employs signal processing in order to detectthe emission signals in a noise floor caused by environmental andintrinsic acoustic signals. The present invention uses signal statisticsto automatically make the decision as to whether the measured signal beregarded as an emission. Specifically, the invention regards each pointof the post-stimulus signal interval separately. Thus statisticallimitations caused by the time distribution of the signals can beavoided. The basic principle is the "history" of a single timelockedpoint during a number of sweeps. In a random signal, its distribution iswell defined on the principles of binomial statistics. A statisticaltest for this single point uses the hypothesis that no time lockedsignal is present. When this hypothesis can be rejected on a 99% levelof confidence, this point can be regarded to be influenced by a stimulusresponse. The invention can be regarded as a device that measures thesignal-to-noise ratio rather than the emission signal only. Itcalculates statistical distributions for 60 points following thestimulus in a time interval from 6 to 12 ms. A "pass" outcome requires 4pairs of alternating positive and negative peaks that meet thesignificance.

Signal Processing for (DPOAE's)

The present invention provides an instrument with phase analysismeasuring capability for distortion product otoacoustic emissions. Anessential feature in the evaluation of distortion products is the factthat the frequencies are known at which an inner ear response isanticipated since these are the intermodulation products of the primaryfrequencies used. Experience shows that the response with the greatestamplitude occurs at a frequency of 2f₁ -f₂ (third order intermodulationproduct), if f₂ is approximately equal to 1.2 times f1.

A typical phase analysis is carried out as follows for this frequency(or other intermodulation products of the primary frequencies used):

1. Signal segments of fixed length are continuously generated for whichthe phases of the two primary signals each have a constant value.

2. These segments are individually subjected to a Fourier transformation(discrete for the selected frequency or FFT). The amount and phase ofthe frequency to be analyzed, and thus the corresponding vector in thephase diagram, are determined.

3. The statistical null hypothesis states:

"The phases of the vectors of all signal segments are uniformlydistributed over the entire angular range between 0 and 360 degrees."

This uniform distribution corresponds with a purely coincidental noisewithout reference to the phases of the primary signal. See FIG. 1.

4. If this null hypothesis can be disproved at a defined significancelevel it may be assumed, given the appropriate significance level, thatthere is a phase-synchronous signal and therefore a response from theinner ear at the frequency analyzed. To do this, the vector's coordinateplane is divided into two halves. The significance test is carried outfor these two halves on the basis of a binomial analysis: every phasevalue is checked to see whether it lies in one half or the other of theco-ordinate plane. In the first case the statistical reference value isincreased by 1, and in the other case decreased by 1. The sum S of thesetwo cases divided by the square root of the number of individualattempts is firmly correlated with the probability that there is only auniform distribution. If, for example, the value S=3.08 is obtained,there is a residual probability of p=0.001 that onlynon-phase-synchronous noise is present in the segments analyzed.

5. Some of the segments analyzed are then used to determine the angle inthe phase diagram by means of which the uniform distribution is tested,i.e. by which the co-ordinate plane is divided. For this, the vector sumof the individual frequency vectors is formed with these segments. Thephase angle of the sum vector+90 degrees (mod 360 degrees) is the angleof the pitch lines through the co-ordinate origin. See FIG. 2 below.

The segments used to calculate the phase angle may not be included inthe statistics described in paragraph 4 for reasons connected with thesignal statistics. Since the analysis is intended to proceedcontinuously, however, in order to achieve an automatic termination whenthe specified significance criterion has been met, the following routeis recommended.

6. The signal segments are used alternately for sum formation to definethe angle and for testing for uniform distribution. Since, therefore,the defined angle changes after every second segment, the angular valuesused for testing must remain stored and must be constantly tested foruniform distribution against the reference angle current at the time.

7. The measurement is terminated

when the significance criterion is met, i.e. if the null hypothesis "No"stimulus synchronous signal present" can be refuted with the previouslydefined significance level or

if the repeatedly recalculated reference phase angle does not convergewithin specified limits, or

if the significance level for refuting the null hypothesis does notreach a specified value after analysis of a specified number of signalsegments.

In the latter two cases (6 and 7), the measurement is terminated with,for example, "Fail" (i.e. no signal from the inner ear could be proved),whereas "Pass", for example, is displayed in the first of the threecases (positive proof of a signal).

Signal Processing for (TEOAE's)

The present invention also provides an instrument with phase analysismeasuring capability for transient evoked otoacoustic emissions. Withtransient evoked otoacoustic emissions, a broad frequency band isemitted. This makes it possible to analyze the phase statistics for anyarbitrary frequency. The statistical testing sequence can consequentlybe the same as that used to detect DPOAE's. A measurement segment istransmitted in which the frequencies to be analyzed are determined.

This can be done as outlined in the following example:

A plurality of intervals is formed in the frequency range (e.g. 500-1000Hz, 1000-2000 Hz, 2000-4000 Hz). The signal segments to be analyzed arealternately written to two buffer stores A and B. The vector of the sumof A and B is then formed for each frequency in accordance withparagraph 5 above. The vector for the difference between A and B is alsocalculated as a reference value. The frequencies in each specifiedinterval in which the greatest difference is found between the vector ofthe buffer sum and that of the buffer difference are analyzed.Thereafter the procedure is exactly the same as that described for thedistortion product otoacoustic emissions in paragraphs 6 and 7 above.

If the measurement is to be terminated with, for example, "Pass", therequirement is that at least one value must meet the specifiedsignificance criterion for each of the specified frequency intervals.

Test Parameters

The method also employs automatic stimulus control. The stimulus levelgenerated by the stimulus generators is optimized for each ear canal andtest run. It should be high enough to obtain a good emission responseand low enough to avoid stimulus artifacts. In a calibration run, thestimulus is checked for amplitude as well as time constancy. Themeasurement will start only if both are acceptable. During measurement,changes in stimulus amplitude are registered and the test is stopped ifit deviates from what was measured during calibration. In this case, a"stimulus unstable" message will appear on the display.

It also employs artifact rejection. Artifacts are defined as signalperiods, which would lower the signal-to-noise ratio if they wereincluded in the averaging procedure. Conventional devices for OAEmeasurement require a manual artifact rejection control duringmeasurement. The optimal artifact threshold is not known in advancebecause the signal-to-noise ratio differs extremely from one individualmeasurement to another. Because of this, the present method tests atdifferent rejection levels simultaneously. As a result testing time isreduced dramatically in most of the cases, especially with restlessinfants.

Follow-Up Procedures

When the method is employed and the apparatus indicates that thesignal-to-noise ratio has not been high enough to prove the presence ofemissions on the required level of significance, a "refer" conditionresults. Because this lack of the required level of significance couldbe attributable to a number of pathologic as well as non-pathologicfactors, follow-up diagnostics should be carried out as soon aspossible. A frequent flickering of the red light during the measurementindicates that the measurement background has been very noisy. In thiscase, it is worthwhile to repeat the measurement. This is especiallytrue when 2 or even 3 pairs of peaks have been detected. Thisinformation is generally displayed on the liquid crystal display (LCD)screen. The further follow-up-procedure is shown in the diagram. Itshould start with the examination of the middle ear status becausemiddle ear dysfunction, which is the most frequent origin of mild tomoderate hearing loss in early childhood.

Thus, the method and apparatus provides an efficient, highly reliablescreening and referral system to test the hearing of newborn infants,which does not require expert evaluators.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical Noise pattern showing a uniform distribution in thevector plane.

FIG. 2 is a Noise pattern superimposed with constant signal in thevector plane.

FIG. 3 is a Block diagram of a screening instrument for the measurement,analysis and evaluation of DPOAE's by means of phase analysis.

FIG. 4 is a Block diagram of a screening instrument for the measurement,analysis and evaluation of TEOAE's by means of phase analysis.

FIG. 5 is a perspective view of a handheld embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The method and apparatus of summary of the invention 10 for audiologicalscreening of infants and newborns described above is incorporated byreference and summarized as follows. It generally comprises firstgenerating a stimulus with acoustic transmitters 12 in both ear canalsof the infant or newborn, and then collecting any transient evoked anddistortion product otoacoustic emissions generated by the cochlea ineach ear canal in response to the stimulus with microphones 13 togenerate a frequency mixed product electronic signal. FIG. 1 is atypical Noise pattern showing a uniform distribution in the vectorplane. FIG. 2 is a Noise pattern superimposed with constant signal inthe vector plane.

FIG. 3 shows a block diagram of an instrument of the invention 10 tomeasure distortion product otoacoustic emissions, which consists of twostimulus generators 11 with the appropriate acoustic transmitters 12.The frequency product generated by the cochlea is measured with the aidof the microphone 13 and fed to an input amplifier 14. The frequenciesof the mixed products are analyzed with the aid of a frequency analyzer15. The phase analyzer 16 contains the means of statistical evaluationreferred to above. The result is shown on a display 17 and/or output toa printer or PC or processed further. The method thus employs twostimulus generators 11 with appropriate acoustic transmitters 12 togenerate sounds impacting the inner ears of an infant or newborn. Theinner ears generate otoacoustic emissions, which are picked up by amicrophone 13 and amplified by an amplifier 15 to generate a frequencymixed product electronic signal.

The microphone 13 electronic signals and the stimulus frequencies arethen inputted into a computer processor consisting of an amplifier 14, afrequency analyzer 15, and a phase analyzer 16. The mixed productelectronic signal is amplified with an input amplifier 14 and analyzedwith the aid of a frequency analyzer 15 and phase analyzer 16 toseparate the frequencies comprising the mixed product electronic signalinto separate background noise signal components and otoacousticemissions signal components.

FIG. 4 shows a block diagram of an instrument of the invention 10 tomeasure transient evoked otoacoustic emissions. It consists of onestimulus generator 19 with the appropriate acoustic transmitter 20. Thefrequency mixture generated by the cochlea is measured with the aid ofthe microphone 21 and fed to an input amplifier 22 and its downstreamfilter 23 and then stored alternately in different memories 24.Automated evaluation is carried out in the vector analyzer 25 by formingsums and differences. The result is shown on a display 26 and/or outputto a printer or PC or processed further. Thus, the frequency analyzer 15associated with the phase analyzer 16 calculates statistical evaluationsof the otoacoustic emissions signal components with binomial statisticsto determine if the otoacoustic emissions signal responses to eachstimulus are or are not statistically significant. These statisticalconclusions are then displayed on a computer display 26.

In summary, the apparatus of the invention 10 is a miniaturized hearingscreening system based upon the measurement of transiently evokedotoacoustic emissions. It consists of a power source (not shown)operably associated with two stimulus generators 11 with the appropriateacoustic transmitters 12. The frequency product generated by the cochleain response to the generated stimulus is measured with the aid of amicrophone 13. The microphone 13 generates an analogue electronic signalfed to an input amplifier 14. The frequencies of the mixed products ofthe electronic signal are analyzed with the aid of a frequency analyzer15 before employing a phase analyzer 16. The phase analyzer 16 isgenerally employed to evaluate the 3^(rd) order intermodulation productlike (2f1-f2), where f2 is approximately equal to 1.2 times f1. Thisprovides the greatest signal amplitude for statistical evaluation asdescribed above. The statistical result is then shown on a "Pass"/"Fail"or "Pass"/"Refer" display 26.

FIG. 5 illustrates a perspective view of a preferred handheld embodimentof the invention 10 approximately 215×100×54 mm. and weighsapproximately 600 grams. It has at least one combination acoustictransmitter/microphone probe 27 structured to generate stimulus in theear canals of the infant or newborn and collecting any transient evokedand distortion product otoacoustic emissions generated by the cochlea inresponse to the stimulus to generate a frequency mixed productelectronic signal. The tip of the probe is covered with a disposablesoft ear insert 28. The transmitter has a sound stimulus level of 70-85dB SPL, and a stimulate rate of between 50 to 100 Hz and ismicroprocessor-controlled. The stimulus type is a non-linear click. Themicrophone has a band width of 1.4 to 4 kHz with maximum sound pressurelimited to 85 dB. The handheld embodiment has a liquid crystal displaywhich indicates artifact rate and stimulus stability. It is batterypowered with a 6 volt/1,000 mAh rechargeable battery giving 6 to 7 hoursof use.

Although this specification has made reference to the illustratedembodiment, it is not intended to restrict the scope of the appendedclaims. The claims themselves recite those features deemed essential tothe invention.

We claim:
 1. A method for audiological screening of infants and newbornscomprising:a. generating one or more stimuli with acoustic transmittersin each ear canal of the infant or newborn, b. collecting any transientevoked and distortion product otoacoustic emissions generated by thecochlea in each ear canal in response to the stimulus with microphonemeans for generating a frequency mixed product electronic signal, c.inputting the frequency mixed product electronic signal from themicrophone means and the stimulus frequencies into a computer processor,d. amplifying the frequency mixed product electronic signal with aninput amplifier, e. computer analyzing the frequencies of a measuredaccoustic signal by means of a frequency and phase analyzer to separatethe different frequencies and phases from one another, f. computerstatistically evaluating the different acoustic signal componentsseparately by means of binomial statistics to determine whether themeasured signal contains stimulus elicited components for each frequencyon a defined level of significance, and g. displaying if the otoacousticsignal response is or is not statistically significant on a computerdisplay.
 2. A method for audiological screening of infants and newbornsaccording to claim 1, wherein the computer statistics evaluation isproved in accordance with criterion with a definable significance level.3. A method for audiological screening of infants and newborns accordingto claim 1, wherein the computer repeatedly statistically evaluates thedifferent accoustic signal components until a predetermined measurementaccuracy significance level is reached.
 4. A method for audiologicalscreening of infants and newborns according to claim 1, wherein themeasured signal is separated into its frequency and phase components bymeans of a Fourier transformation.
 5. A method for audiologicalscreening of infants and newborns according to claim 4, wherein thevector sum of each selected frequency component in a complex twodimensional space is calculated to formulate a null hypothesis anddetermine a preferred direction in the complex space.
 6. A method foraudiological screening of infants and newborns according to claim 5,wherein the complex two dimensional space is divided into two distinctareas corresponding to the preferred direction in the complex spacecalculated from the vector sum null hypothesis method.
 7. A method foraudiological screening of infants and newborns according to claim 5,wherein the phase vectors of the Fourier transforms of the individualsignal segments are each assigned to one of the two areas, and areanalyzed with mathematical means of a binomial statistical analysis. 8.A method for audiological screening of infants and newborns according toclaim 4, wherein the signal components are assigned a particular qualitycategory.
 9. A method for audiological screening of infants and newbornsaccording to claim 8, wherein a separate mathematical analysis iscarried out for each quality category.
 10. A method for audiologicalscreening of infants and newborns according to claim 1, wherein theresults of the computer calculations are displayed in the form of curveson a computer display screen.
 11. A method for audiological screening ofinfants and newborns according to claim 1, wherein the computer is ahand-held, self powered, portable microprocessing unit.
 12. A method foraudiological screening of infants and newborns according to claim 1,wherein the results of the computer calculations are displayed via aprinter interface.
 13. A method for audiological screening of infantsand newborns according to claim 1, including a personal computer systemconnected via an interface for further evaluation of the results.
 14. Anapparatus for audiological screening of infants and newbornscomprising:a. at least one acoustic transmitter structured forgenerating one or more stimuli at sound frequencies, which generateresponsive otoacoustic emissions in both ear canals of the infant ornewborn, b. at least one microphone adapted to be removably placed inboth ear canals for collecting any transient evoked and distortionproduct otoacoustic emissions generated by the cochlea in each ear canalin response to the stimulus to generate a frequency mixed productelectronic signal, c. a computer processor with memory and a centralprocessing unit programmed with statistical processing instructions tostatistically evaluate acoustic signal components by means of binomialstatistics to determine whether a measured signal contains stimuluselicited components for each frequency on a defined level ofsignificance, d. input means associated with the microphones forinputting the frequency mixed product electronic signals from themicrophones and the stimulus frequencies into the computer processor, e.amplifier means associated with the computer processor for amplifyingthe frequency mixed product electronic signal, f. a frequency analyzerand phase analyzer associated with the computer processor to analyze ameasured acoustic signal and separate the different frequencies andphases from one another, g. display means for displaying if theotoacoustic signal responses are or are not statistically significant,and h. a power source associated with the computer components,microphones, transmitters, amplifiers, and display means to drive thesame.
 15. An apparatus for audiological screening of infants andnewborns according to claim 14, including different sized disposableinserts covering the microphones such that the covered microphone isadapted to be easily inserted within the ear canals of newborns andinfants.